The present invention relates to methods of hydrogenating liquid-coal intermediates and products such as those produced in conventional coal liquefaction processes and solvent refined coal processes. For purposes of this application the term "coal liquid" is intended to include carbonaceous liquids derived from anthracite, bituminous, and lignite coal as well as similar liquids from peat, oil shale, tar sand, wood, lignin, solid petroleum residuals and other related materials.
The coal liquids produced by well-known coal liquefaction processes include a mixture of aromatic compounds including but not limited to benzene, naphthalene, anthracene, methylindan, decalin and derivatives of these compounds. Tars, bitumens, asphaltenes, other higher boiling compounds and ash may also be included. It is desirable to further hydrogenate these coal liquids and separate them from solid materials to make them suitable for use as fuel oils and feed stock for the production of refined fuels.
Previous methods for hydrogenating and liquefying coal and coal liquids have included the use of heterogeneous catalysts. Solid catalysts including compounds of cobalt, iron, nickel, molybdenum or tungsten deposited on silico-aluminates or other appropriate supports are contacted with the coal liquid in the presence of hydrogen or a suitable hydrogen donor in solution. Molten salts such as zinc chloride also are employed as catalysts. Such heterogeneous systems must include sufficient reaction surfaces available to both the hydrogen and the coal liquid to allow the reaction to proceed at an acceptable rate. Much more intimate contact is possible with homogeneous systems in which the catalyst is dissolved within the liquid undergoing hydrogenation. However, in the homogeneous systems, the separation of product and catalyst has been an extremely difficult problem.